Straight and rigid flagellar hook made by insertion of the FlgG specific sequence into FlgE.

The bacterial flagellar hook connects the helical flagellar filament to the rotary motor at its base. Bending flexibility of the hook allows the helical filaments to form a bundle behind the cell body to produce thrust for bacterial motility. The hook protein FlgE shows considerable sequence and structural similarities to the distal rod protein FlgG; however, the hook is supercoiled and flexible as a universal joint whereas the rod is straight and rigid as a drive shaft.

Identical folds used for distinct mechanical functions of the bacterial flagellar rod and hook.

The bacterial flagellum is a motile organelle driven by a rotary motor, and its axial portions function as a drive shaft (rod), a universal joint (hook) and a helical propeller (filament). The rod and hook are directly connected to each other, with their subunit proteins FlgG and FlgE having 39% sequence identity, but show distinct mechanical properties; the rod is straight and rigid as a drive shaft whereas the hook is flexible in bending as a universal joint. Here we report the structure of the rod and comparison with that of the hook.

Assembly and stoichiometry of FliF and FlhA in Salmonella flagellar basal body.

The bacterial flagellar export apparatus is required for the construction of the bacterial flagella beyond the cytoplasmic membrane. The membrane-embedded part of the export apparatus, which consists of FlhA, FlhB, FliO, FliP, FliQ and FliR, is located in the central pore of the MS ring formed by 26 copies of FliF. The C-terminal cytoplasmic domain of FlhA is located in the centre of the cavity within the C ring made of FliG, FliM and FliN.

Distinct roles of highly conserved charged residues at the MotA-FliG interface in bacterial flagellar motor rotation.

Electrostatic interactions between the stator protein MotA and the rotor protein FliG are important for bacterial flagellar motor rotation. Arg90 and Glu98 of MotA are required not only for torque generation but also for stator assembly around the rotor, but their actual roles remain unknown. Here we analyzed the roles of functionally important charged residues at the MotA-FliG interface in motor performance.